Application Research Of PHC Pipe Pile In Collapsible Loess

In recent years, prestressed high strength concrete piles (PHC piles) because of itshigh carrying capacity, good pile driving quality, the fast construction speed, littleenvironmental pollution and many other advantages, are in good graces of all theengineering community, and applied in soft coastal land area, which obtain a greatsuccess. But, in inland loess areas, the application of PHC pile is short and theoreticalresearch is backward in engineering practice, especially for the research results of the pilefriction can no longer meet the needs of the actual project. The pile load-settlementcurve of non-destructive static load test is slowly varying and ultimate vertical bearingcapacity of a single pile is not easy to determine in the loess region due to lithologicdifferences and other reasons. At the same time, when PHC pile used in loess areas, it isnecessary to consider the influence of pile side negative skin friction to the calculation ofthe vertical bearing capacity. Therefore, the PHC pile in collapsible loess has sometheoretical significance and practical value.In this paper, on the basis of summarizing the results of the vertical bearing capacitytheory, it focused on analyzing the influence of the pile side resistance,"squeezing effect"and "the soil plugging effect" to vertical bearing capacity. It detailed describedmechanism of down drag due to collapsibility of loess, and showed common methods toeliminate loess collapsibility and its scope of application. Combined with fieldmeasurement data to systematic analyze the vertical bearing capacity, it used polynomialfitting to calculate the ultimate vertical bearing capacity of a single pile that the load-settlement curve is slow variation. Using ABAQUS finite element software to simulatethe process of pile load settlement, to explore the distribution of the pile lateral frictionand the soil plug-effect mechanism at pile tip and determine the ultimate vertical bearing capacity by the final analog. By the comparative analysis of the numerical simulationresults and fitting results, verifying the results calculated by the polynomial fittingmethod is reliability. The conclusion showed that ultimate vertical bearing capacitywhich back-stepping by polynomial fitting is relatively close to the numerical simulationresults, and more consistent with the actual situation, besides it can effectively solve theproblem of the slow variant Q-S curve of the ultimate vertical bearing capacity difficultto determine and provide reference for similar engineering geological conditions in thefuture design and calculation of ultimate vertical bearing capacity of a single pile.